Electrical control apparatus, including two condition responsive means



Dec. 25, 1956 J. M. WILSON 2,775,291

ELECTRICAL CONTROL APPARATUS, INCLUDING TWO CONDITION RESPONSIVE MEANS Filed Feb. 15, 1954 r! LINE [8 LINE 1 95 37 as g 2a 27 I i A LIMIT I l v 5mm n my CONTROL L INVENTOR.

JOHN M. WILSON ATTORNEY United States PatentfO ELECTRICAL CONTROL APPARATUS, INCLUD- ING TWO CONDITION RESPONSIVE MEANS John M. Wilson, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application February 15, 1954, Serial No. 410,37 8

9 Claims. (Cl. 15828) The present invention is concerned with the control apparatus for a fuel burner in which afirst and a second separate electronic flame detector are used to detect the presence of flame at a burner unit, and in which the action of the'first and second electronic flame detector is so interlocked to prevent operation of the burner unit if one of the first or second electronic flame detectors fail.

Electronic flame detectors are very desirable for use in monitoring combustion flames since these flame detectors can be designed to be very fast acting and can therefore render the burner unit inoperative substantially immediately upon the failure of flame at the burner unit and thereby preventing the feeding of raw fuel into the fire box. However, even with the simplest electronic flame detector there are a number of components which can fail and result in either a safe or an unsafe failure of the electronic flame detector. An unsafe failure is a failure which causes the electronic flame detector to continuously indicate the presence of flame independent of the actual existence of the flame. A safe failure is a failure which causes the electronic flame detector to continually indicate the absence of flame independent of the actual condition of the flame.

It is an object of the present invention to provide a control apparatus wherein failure of one of two flame detectors in either a safe or an unsafe condition will render the control apparatus inoperative.

It is a further object of the present invention to provide a first electronic flame detector having a first flame relay which is energized in the presence of flame and a second electronic flame detector having a second flame relay which is deenergized in the presence of flame, "with the switches controlled by the first and second relay being so interconnected as to prevent initial energization of the control apparatus if one of the flame detectors fails unsafe and to prevent continued operation of the burner being controlled if one of the flame detectors fails. safe.

The single figure is a schematic showing of a fuel burner system incorporating the present invention.

Referring to the single figure, the numeral 10 designates a fuel burner unit having a main burner 11, a main burner valve 12, a pilot burner 13 located in igniting relationship to the main burner 11, a pilot valve 14, an ignition transformer 15, and a flame detection means, or flame rod 16.

A thermostat 17 is provided and is adapted to be located in the space to be heated by the burner unit 10. Upon a need for operation of the burner unit 10, the thermostat 17 is operative to cause engagement between a switch blade 18 and a contact 19.

Operation of thermostat 17 directly controls a main burner control relay 20 having a Winding 21, movable switch blades 22 and 23, and stationary contacts 24, 25, and 26. Movable switch blade 22 is biased, by means not shown, to normally engage stationary contact 25. Upon energization of winding 21 of relay 20, movable switch blade 22 disengages stationary contact 25' and 2 ,7 ,291 Patented Dec. 25, .1956

' 2 engages stationary contact 24 while movable switch blade 23 engages stationary con-tact 26.

Energization of winding 21 of relay 20 is elfected by means of a transformer 27 having a primary 28 and a secondary 29 having a tap 30. Also included in the energizing circuit for the relay 20 is a safety cutout device 31 having a bimetal actuator 32, a heater 33, normally engaged contacts 34 and 35, and having a reset actuator 36. The action of cutout device is such that a predetermined time period of energization of heater 33 causes bimetal 32 to warp to the left out from under contact 35. Contact 35 is biased downward and disengages contact 34. Upon cooling of bimetal 32, the contacts 34 and 35 may be reset to engaged position by depressing actuator 36.

It will be noted that the energizing circuit for the primary 28 of transformer 27 includes a limit control 37. This limit control is normally in circuit closing position and is operative only upon an improper condition' occuring at the burner unit 10, for example an eX- cessively high temperature occasioned by an excessively long period of operation of the main burner 11, to move to open circuit condition to deenergize transformer 27.

A first electronic flame detector is designated by the reference numeral 38 and includes electron discharge devices 39 and 40. This electronic flame detector is of the type flame detector shown in the Richard S. Feigal Patent 2,556,961. The operation of this electronic flame detector is fully described in the above mentioned Richard S. Feigal patent, however, the operation will be briefly outlined here.

Electronic flame detector 38 includes a conductor 41 which is adapted to be connected to a flame sensing device such as a flame rod or photocell, it being shown connected to the flame rod 16 in the present instance. In the absence of a flame impinging upon the flame electrode 16, the discharge device 39 is substantially conductive and a biasing voltage is developed across resistor 42 of apolarity shown in the figure. This biasing voltage renders the discharge device 48 substantially non-conductive. A relay 43 is provided in the output circuit of the electronic flame detector 38 and is therefore deenergized in the absence of flame at the flame electrode 16. If it is now assumed that a flame impinges upon the flame electrode 16, the electron discharge device 39 is rendered less conductive and therefore the biasing voltage developed across resistor 42 no longer exists. Discharge device 40 is therefore rendered conductive and relay 43 isenergized.

Relay 43 includes a coil 44, movable switch blades 45, 46, 47, and 48, and stationary contacts 49, 50, 51, and 52. The movable switch blades 46 and 48 are biased, by means not shown, to engage stationary contacts 50 and 52 respectively and movable switch blades 45 and 47 are biased, by means not shown, to be disengaged from the stationary contacts 49 and 51 respectively. Upon energization of relay winding 44 movable switch blades 45 and 47 move into engagement with stationary contacts 49 and 51 respectively and movable switch blades 46 and 48 disengage stationary contacts 50 and 52 respectively.

Power is supplied to electronic flame detector 38 by means of a transformer 53 having a primary 54 and a secondary 55. The cathodes of discharge devices 39 and 40 are heated by a secondary of transformer 53, which secondary has not been shown.

A second electronic flame detector is designated by the reference numeral 56 and includes an electron discharge device 57. Electron discharge device 57 includes an anode '58, a control electrode 59, and a cathode 6 0.

Power is furnished to the second electronic flame detector 56 by means ofa transformer 64 having a primary 65 and a secondary 66. The cathode of discharge device 57 is heated by a secondary of transformer 64, which secondary is not shown. The left hand end of the secondary 66 is grounded at ground connection 67. Located in the plate to cathode circuit of the discharge device 57 is a relay 68 having a winding 69, movable switch blades 70 and 71, and stationary contacts 72 and 73. The movable switch blades 70 and 71 of relay 68 are shown in their energized position, that is with movable switch blade 70 engaging stationary contact 72. In the deenergized condition of relay 68, movable switch blade 71 is biased, by means not shown, to engage stationary contact 73 and movable switch blade 70 is biased to disengage stationary contact 72.

Directly connected across the secondary 66 is a series combination of a capacitor 74, a resistor 75, and a resistor 76. Electronic flame detector 56 includes a conductor 77 which is adapted to be connected to a flame detection device such as a flame rod or a photocell, and is shown connected to the flame rod 16.

The operation of electronic flame detector 56 can be explained as follows. In the absence of flame at the flame rod 16 the control electrode 59 of the discharge device 57 is at substantially the same potential as the cathode 60 and the discharge device 57 is rendered conductive. Since the coil 69 of relay 68 is located in the anode to cathode circuit of discharge device 57, relay 68 is energized and the movable switch blades 70 and 71 assume the energized position as shown in the figure. If it is now assumed that a flame impinges upon flame electrode 16 a direct current voltage is established across capacitor 74 of a polarity such that the lower plate of the capacitor is negative with respect to the upper plate. This direct current voltage is established across capacitor 74 due to the rectifying characteristics of the flame. Since the main burner 11 and the pilot burner 12 are grounded at ground connections 79 and 78, respectively, electron current flow can be traced from the left hand end of secondary 66 through ground connection 67, ground connection 78 or 79, the flame, flame rod 16, conductor 77, a capacitor 74 to the right hand end of secondary 66. This electron current flow establishes the above mentioned voltage across capacitor 74. This voltage is distributed through resistors 75 and 76 to render the control electrode 59 of discharge device 57 negative with respect to cathode 60. This voltage is operative to render the discharge device 57 substantially non-conductive to thereby deenergize relay 68 upon the presence of flame at the flame rod 16.

Operation The overall operation of the improved control apparatus may now be considered. The single figure shows the control apparatus in the standby condition. That is, main burner control relay 20 is deenergized, relay 43 is deenergized, indicating that electronic flame detector 38 is properly indicating the absence of flame at the flame rod 16, and relay 68 is energized, indicating that flame detector 56 is properly indicating the absence of flame at the flame rod 16.

If it is now assumed that there is a need for operation of the fuel burner unit 10, the thermostat 17, which is located in the space to be heated, moves to the circuit closing position and switch blade 18 engages contact 19. An energizing circuit can now be traced for relay 20 from the right hand end of secondary 29 through conductor 80, contacts 34 and 35 of safety cutout device 31, winding 21 of relay 20, conductor 81, thermostat 17, conductor 82, conductor 83, movable switch blade 46 and stationary contact 50 of relay 43, conductor 84, movable switch blade 70 and stationary contact 72 of relay 68, conductor 85, conductor 86, heater 33 of safety cutout device 31, and conductor 87 to the left hand end of secondary 29. From the above traced circuit it can be seen that the initial energizing circuit for relay 20 depends upon relay 43, controlled by flame detector 38, being deenergized and upon relay 68, controlled by flame detector 56, being energized. If either flame detector 38 or flame detector 56 fails in an unsafe condition and improperly indicates that there is a flame at this time, the above mentioned energizing circuit for relay 20 cannot be completed.

Energization of relay 20 causes movable switch blade 23 to engage stationary contact 26. An energizing circuit is now established for pilot valve 14 and this circuit can be traced from a power line conductor 88 through limit cotrol 37, conductor 89, stationary contact 26 and movable switch blade 23 of relay 20, conductor 90, conductor 91, conductor 92, pilot valve 14, conductor 93, and conductor 94 to a second power line conductor 95. An energizing circuit for ignition transformer 15 can also be traced from power line conductor 88 through limit control 37, conductor 89, stationary contact 26 and movable switch blade 23 of relay 20, conductor 90, conductor 96, stationary contact 52 and movable switch blade 48 of relay 43, conductor 97, and ignition transformer 15 to power line conductor 95. Therefore, fuel issues from pilot burner 13 and is ignited by the ignition transformer 15.

Energization of relay 20 also causes movable switch blade 22 to move to disengage stationary contact 25 and to engage stationary contact 24. The function of this switching action will be described later.

With pilot flame established at pilot burner 13, a flame impinges upon flame rod 16 and affects the flame detectors 38 and 56 in the manner above described. Namely, the relay 43 is energized and the relay 68 is deenergized. The above traced initial energizing circuit for relay 20 required that the relays 43 and 68 be deenergized and energized respectively and it would appear that relay 20 is now deenergized. However, movable switch blades 45 and 46 of relay 43 are overlapping. That is, movable switch blade 45 engages stationary contact 49 before movable switch blade 46 disengages stationary contact 50. A holding circuit for relay 20 can now be traced from the right hand end of secondary 29 through conductor 80, contacts 34 and 35 of safety cutout device 31, winding 21 of relay 20, conductor 81, thermostat 17, conductor 82, stationary contact 24 and movable switch blade 22 of relay 20, conductor 100, stationary contact 49 and movable switch blade 45 of relay 43, and conductor 101 to the tap 30 on secondary 29. It can be seen at this time that the holding circuit for relay 20 does not include the heater 33 of safety cutout device 31. and therefore heating of bimetal 32 ceases at this time.

Energization of relay 43 of electronic flame detector 38 causes movable switch blade 48 to disengage stationary contact 52. This switch blade is in the above traced energizing circuit for ignition transformer 15 and the ignition transformer is deenergized at this time. Movable switch blade 46 disengages stationary contact 50 and breaks the above traced initial energizing circuit for relay 21). The action of movable switch blade 47 in moving into engagement with stationary contact 51 is shown below.

Denergization of relay 68 of electronic flame detector 56 causes movable switch blade 70 to disengage stationary contact 72. This breaks the above traced initial energizing circuit for relay 20 which is also broken at movable switch blade 46 and fixed contact 50 of relay 43. Movable switch blade 71 moves into engagement with stationary contact 73 and completes an energizing circuit for the main fuel valve 12. This energizing circuit can be traced from the power line conductor 88 through limit control 37, conductor 89, stationary contact 26 and movable switch blade 23 of relay 20, conductor 90, conductor 91, conductor 110, movable switch blade 47 and stationary contact 51 of relay 43, conductor 111, stationary contact 73 and movable switch blade 71 of relay 68, conductor 112, main fuel valve 12, and conductor 94 to the powerline conductor 95. This above traced energizing circuit causes the main fuel valve 12 to open and admit fuel to the main burner 11.

From the above traced circuit it can be seen that in order for fuel valve 12 to be energized it is necessary for relay 43 to be energized, indicating that flame detector 38 is properly detecting flame at pilot burner 13, and it is necessary that relay 68 be deenergized, indicat ing that the flame detector 56 is properly indicating the presence of flame at the pilot burner 13.

The apparatus is now in the running condition, that is with the main burner control relay 20 energized, the heater 33 of safety cutout device 31 deenergized, relay 43 of electronic flame detector 38 energized, and relay 68 of electronic flame detector 56 deenergized.

If during the running operation of the burner unit there is a safe failure in either of the flame detectors 38 or 56 such that the flame detectors can no longer indicate flame when in fact a flame is present at the burner unit 11, relay 43 is deenergized and relay 68 is energized. This breaks the above traced energizing circuit to the main fuel valve 12 and therefore causes the flame at the main burner 11 to be extinguished.

If either of the electronic flame detectors 38 or 56 fail in an unsafe condition so that one of the relays or 68 remain energized independent of whether or not the flame actually exists at the burner unit 10, the control apparatus continues to function as if it were operating properly and the flame is then monitored by the remaining flame detector which is operating properly.

However, if such an unsafe failure occurs the apparatus will sense this unsafe failure upon the next call for operation of burner unit 10 by thermostat 17. This can be shown by assuming that the thermostat 17 opens the circuit from switch blade 18 to stationary contact 19.' This deenergizes the main burner control relay 2t) and causes movable switch blade 23 to disengage stationary contact 26. This cuts off all power to the burner unit 10. It will further be assumed that the space in which the thermostat 17 is located cools to a point where the thermostat again closes the circuit from movable switch blade 18 to stationary contact 19. If an attempt is now made to trace the above traced initial energizing circuit for relay it will be found that this initial energizing circuit is open circuited at the relay 43 or 63 associated with electronic flame detector in which an unsafe failure has occured. Therefore, the burner unit 10 cannot be energized even though the thermostat 17 is indicating a need for operation of the burner unit.

If an unsafe failure occurs in the electronic flame detector 38 the relay 43 is improperly energized when relay 20 is deenergized and in this condition an energizing circuit can be traced for heater 33 of safety cutout device 31. This energizing circuit can be traced from the left hand end of secondary 29 through conductor 87, heater 33, conductor 86, conductor 120, stationary con tact and movable switch blade 22 of relay 20, conductor 100, stationary contact 49 and movable switch blade 45 of relay 43, and conductor 101 to the tap 3% of secondary 29. Therefore, the heater 33 of safety cutout device 31 is operative to cause the bimetal 32 to warp to the left out from under the contact 35 and the contact 35 disengages the contact 34 to also open the above traced initial energizing circuit for relay 20.

With such an unsafe failure in either of the electronic flame detectors 38 or 56, it is necessary for the fault to be corrected before the fuel burner unit 10 can again be rendered operative upon a call for heat by the thermostat 17.

From the above description it can be seen that an improved control apparatus has been provided wherein a first and a second electronic flame detector are so interconnected to provide safe operation of the burner unit being controlled even though there may be a failure within either of the electronic flame detectors.

I claim as my invention:

1. Control apparatus for a :fuel "burner 'unit'comprising, a first electrically operable flame detector including a first relay having switch means and having acoil adapted to be energized upon said first flame detector detecting flame at the fuel burner unit, a second electrically operableflame detector including a second relay having switch means and having a coil adapted to be de-energized upon said second flame detector detecting flame at the fuel burner unit, a control relay having switch means and a coil, initial energizing circuit means for said control relay coil includingsaid first'andsecond relay switch means and adapted to be completed when said first relay coil is deenergized and said second-relay coil is energized, and a control circuit including said first second relay switch means and said controlrelay switch means and adapted to be connected to an electrically operable fuel controlfor the fuel burner unit and completed only when said first relay coil is in energized-condition and said second relay coil is in de energized' condition and said control relaycoil is in energized condition.

2. Control apparatus "for a fuel burner h-avinga pilot burner comprising, a first relay having-a coil and a nortmal-ly open switch which is closed when said first relay coil is energized and which'i's adapted to energize a control valve for a pilot burner, a first electronic flame detector adapted to detect flame atithe fuel and pilot burners, .a second relay having a coil connected to said first flame detector in such a manner as to be energized upon said first flame detector detecting flame, :a first switch controlled by said second relay and arranged to be closed when said second relay'coil is de-energized, a second switch controlled bysaid second relay and arranged to be closed when said secondrel-ay coil is energized, a second electronic flame detector adapted to detect flame at the fuel and pilot burners, a third' relay having acoil connected to said second flame detector in such a manner as to be de-energized upon sa-idisecond flame detector detecting flame, a first switch controlled by said third relay and arranged to be closed when said third relay coil is de-energized, a second switch controlled by said third relay and arranged to be closed when-said'third relay coil is energized, an initial energizing circuit for saidfirst relay coil including a series connection of the first switch of'said second relay and the second switch of said third relay so that said first relay coil can be energized only when said second relay coil is'de-energized and said third relay coil is energized in response to both said first and second flame detectors detecting the absence of flame, and

an energizing circuit adapted to be connected to an electrically energiza-ble valve for the fuel burner and including a series connection of the second switch of said second relay and the first switch of said third relay so that said energizing circuit can be completed only when said flame sensing means arranged to sense flame at the'fue'l burner unit, a first and a second electronic amplifier each having an input, means connecting the input of said first and second amplifiers to said flame sensing means to enable a signal to be applied to said inputs indicative of the presence or absence of flame, said first amplifier including a first electron discharge device having a control electrode and an anode and cathode, meansb-ias-ing said control electrode to render said first discharge device substantially nonconduct-ive when a signal indicative of no flame is applied to the input of said first amplifier, a first relay having a oil connected in circuit with the anode and cathode of said first discharge device, said first relay coil thereby being energized upon a signal indicative of flame being applied to the input of said first amplifier, said second amplifier including a second elecanode and cathode, means biasing said control electrode to render said second discharge device substantially nonconductive when .a signal indicative of flame is applied to the input of said second amplifier, a second relay having a coil connected in circuit with the anode and cathode of said second discharge device, said second relay coil thereby being de-energized upon a signal indicative of flame being applied to the input of said second amplifier, and circuit means including switches controlled by said first and second relay-s adapted to be connected to an electrically energizable fuel control for the fuel burner unit and arranged to be completed only when both said first and second amplifiers are properly responding to flame to energize said first relay coil and de-energize said second relay coil.

4. Burner control system comprising, a main fuel burner, an electrically energizable valve controlling the flow of fuel to the main fuel burner, a pilot burner arranged in igniting relationship to said main fuel burner, a main relay having a coil adapted to be energized upon a need for operation of said main burner, a source of electrical power, a first electrically operable flame detector arranged to detect flame at said pilot and main burner and having a first relay with a coil which is ener-gized upon said first flame detector detecting flame, a second electrically operable flame detector also arranged to detect flame at said pilot and main burner and having a second relay with a coil which is de-energized upon said second flame detector detecting flame, circuit means including switches controlled by said first and second relays and adapted to connect said main relay coil to said source of power upon a need for operation of said main burner only when both said first and said second flame detectors are detecting the absence of flame, circuit means control-led by a switch of said main relay in energized condition to cause fuel to flow to said pilot burner and to he ignited, and circuit means including switches controlled by said first and second relays and adapted to connect said valve to said source of power only when both of said first and second flame detectors are detecting the presence of flame.

5. Control apparatus for use with a burner unit having a pilot burner, an electrically energizable pilot valve, a main burner, and an electrically energizable main valve, comprising; a firs-t amplifier having an input and having an output circuit including first current responsive switching means, the current flow in said output circuit being substantially zero in the absence of a signal at said input, .a second amplifier having an input and having an output circuit including second current responsive switching means, the current flow in the output circuit of said second amplifier being substantially zero in the presence of a signal at the input of said second amplifier, a flame detecting device adapted to detect flame at the pilot and main burners, means connecting said flame detecting device to the inputs of both of said first and second amplifiers to enable a control signal to be applied to said inputs upon the presence of flame at the pilot or main burner, means including switches controlled by said first and second current responsive switching means adapted to energize the pilot valve only when both said first and second amplifiers are responding to the lack of a signal at the input of said first and second amplifier, and circuit means including further switches controlled by said first and second current responsive switching means adapted to energize the main valve upon both said first and second amplifiers responding to the presence of a signal at the input of said first and second amplifiers.

6. Control apparatus for use with a fuel burner unit having a main electrically energizable valve, comprising; electronic flame sensing means having a first and a second signal circuit, each circuit having a separate input and a separate output, a pair of relays each having switch means and each having a coil, means connecting said relay coils one to each of the outputs of said signal circuits, a flame responsive element adapted to be positioned to respond to flame at the fuel burner unit, means connecting said flame responsive element to said inputs of said first and second circuits, a further relay having a coil and switch means, an energizing circuit for said further relay coil including the switch means of said pair of relays and adapted to be completed only when the coil of one of said pair of relays is energized and the coil of the other of said pair of relays is de-energized, and an energizing circuit for control of the main valve including the switch means of said pair of relays and the switch means of said further relay and adapted to be completed only when said one relay coil is de-energized, said other relay coil is energized and said further relay coil is energized.

7. Control apparatus for a fuel burner unit having electrically energizable pilot and main fuel valves, comprising; first electrically operable flame detection means including a first relay having a coil which is energized when said first flame detection means detects flame at the fuel burner unit, a plurality of switches controlled by said first relay, second electrically operable flame detection means including a second relay having a coil which is de-energized when said second flame detection means detects flame at the fuel burner unit, a plurality of switches controlled by said second relay, control means having an electrically energizable actuator and switch means controlled thereby, initial energizing circuit means for said actuator adapted to be connected to means responsive to the need for fuel burner operation, said energizing circuit means including a switch controlled by said first relay which is closed when said first relay coil is de-energized and including a switch controlled by said second relay which is closed when said second relay coil is energized, an energizing circuit adapted to be connected to the pilot fuel valve, said energizing circuit including said control means switch means; and a further circuit adapted to be connected to the main fuel valve, said further circuit including a switch controlled by said first relay which is closed when said first relay coil is energized, including a switch controlled by said second relay which is closed when said second relay coil is de-energized and including said control means switch means.

8. Control apparatus comprising; a first electronic flame detector having a first electron discharge device having a control electrode and an anode and cathode, means connected to said control electrode and adapted to bias said first discharge device substantially to cutoff upon said first flame detector detecting the absence of flame at a predetermined point, a first relay having a coil connected in circuit with said anode and cathode to be energized when said discharge device is substantially conductive; a second electronic flame detector having a second electron discharge device having a control electrode and an anode and cathode, means connected to said control electrode of said second discharge device to bias said second discharge device substantially to cutoff upon said second flame detector detecting the presence of flame at the predetermined point, a second relay having a coil connected in circuit with said anode and cathode of said second discharge device to be energized when said second discharge device is substantially conductive; control means having an electrically energizable actuator, initial energizing circuit means for said actuator including switches controlled by said first and second relays and adapted to be completed only when said first relay coil is tie-energized and said second relay coil is energized, and further circuit means including further switches controlled by said first and second relays and by said control means and adapted to be completed only when said first relay coil is energized, said second relay coil is de-energized and said actuator is energized.

9. Control apparatus for use with condition establishing means for establishing a given condition, comprising; a first electrically operable condition responsive means including a first relay having switch means and a coil controlled by said first condition responsive means and adapted to be energized upon said first condition responsive means responding to the condition established at the condition establishing means, a second electrically operable condition responsive means including a second relay having switch means and a coil controlled by said second condition responsive means and adapted to be de-energized upon said second condition responsive means responding to the condition established at the condition establishing means, a control relay having switch means and a coil, initial energizing circuit means for said control relay coil including said first and second relay switch means and adapted to be completed when said first relay coil is de-energized and said second relay coil is energized, and a further circuit for controlling the condition estab- References Cited in the file of this patent UNITED STATES PATENTS 2,230,732 Tapp et al. Feb. 4, 1941 2,427,178 Aubert Sept. 9, 1947 2,431,158 Yates Nov. 18, 1947 2,440,700 Rosche May 4, 1948 2,616,490 Wilson Nov. 4, 1952 2,632,102 Iellinek Mar. 17. 1953 

